Polymers formed from diallyl dialkyl ammonium monomers have a wide variety of uses. The cationic polymers, for example, can be used as flocculants or coagulants in water and sewage treatment systems. It has been shown that the higher the molecular weight of the resulting cationic polymer, the more effective the polymer is as a flocculating or coagulating agent.
However, homopolymers formed from diallyl dialkyl ammonium monomers do not readily polymerize to produce high molecular weight polymers. When attempts have been made to make high molecular weight products, agglomeration may result during the suspension or emulsion polymerization; insolubles may form indicating too much crosslinking which seriously interferes with application effectiveness and decreasing water-solubility of the final polymer products; and low monomer conversion may leave more than about 5 wt % residual monomer limiting the applicability of the final high molecular weight formed diallyl dialkyl ammonium polymer.
Despite the wealth of literature on diallyl dimethyl ammonium chloride (DADMAC) polymers, there is little in the art showing the preparation of polyDADMAC (homopolymer of DADMAC) with ultra high molecular weight.
Japanese Patent 56-18611 exemplifies a polyDADMAC having intrinsic viscosity 4.07 dl/g (at 30° C. in a 5% aq. NaCl soln.) and solution viscosity (0.5% solids in H2O) 305 cP at 20° C. The procedure of the Japanese process involved using a polymerization time of one week at low temperatures. This process is obviously not commercially feasible. Furthermore, the polyDADMAC formed is a gel not a bead.
U.S. Pat. No. 5,248,744 discloses a process for the polymerization of DADMAC in an aqueous solution. The polymers disclosed show an intrinsic viscosity varying from 0.87 to 2.07 dL/g measured in 1.0 M sodium nitrate. This reference requires the slow addition of initiator at two points during the polymerization of DADMAC.
U.S. Pat. No. 5,185,411 discloses a two phase process for synthesizing PolyDADMAC beads by inverse suspension polymerization. The examples record a weight average molecular mass ranging from 1,340,000 g/mole to 2,340,000 g/mol. No description of the method for measuring the molecular weight is given. The percent conversion varies from 87.4 to 94.7 weight %. The process disclosed uses less than 1 wt. % of initiator based on the total weight of monomer.
Copolymers of DADMAC with other monomers, such as acrylamide are well known in the art. For example, U.S. Pat. No. 4,713,431 discloses high molecular weight DADMAC copolymers by emulsion polymerization of DADMAC with small amounts of acrylamide. Acrylamide monomer has a reactivity much higher than DADMAC and is known to produce polymers with a molecular weight much higher than that of DADMAC. These copolymers with acrylamide level from 0.44 to 13 wt. % show intrinsic viscosities which vary from 1.7 dL/g to 4.6 dL/g. The copolymers with acrylamide level lower than 1 wt. % have an intrinsic viscosity lower than 2.0 dL/g. The emulsion copolymers contain high residual DADMAC monomer of more than 7 wt. %. For many applications however, DADMAC hompolymers are preferred to copolymers.
U.S. Published Application No. 2004/0030039 discloses a polymerization process for the preparation of polyDADMAC nodules with high bulk viscosities at 20 wt. % (20% BV) ranging from 11,500 cps to 97,000 cps. The reference assumes a linear relationship between 20% BV and molecular weight with the proportionality factor based on the measured molecular weight of 100,000 polyDADMAC.
The process disclosed in this reference requires a specific high initial monomer concentration range of from 67 to 77%. The reaction producing the alleged high molecular weight polyDADMAC is run for several hours at a temperature of about 60° C. The molecular weight of the polyDADMAC formed in U.S. Published Application No. 2004/0030039 is measured using 20% BV. In contrast, the polyDADMAC formed in the present invention is of such high molecular weight that values of 20% BV are too concentrated and produce much higher bulk viscosities than 10,000 cps, and can not be conveniently measured using 20% BV.
In the present invention, bulk viscosity of a polymer solution in water at a concentration of, preferably, 1.0 wt %, and at a temperature of 25° C. is used to indicate the MW of polyDADMAC.
Surprisingly the inventors have made a polyDADMAC of high bulk viscosity at 1% polymer concentration (1% BV) of greater than 20 cps distinguished from known commercial polyDADMAC products. Additionally, the Inventors have accomplished this by a method which polymerizes DADMAC in high conversion without aggregation problems commonly associated with suspension polymerization and emulsion polymerization.
The ultra high molecular weight polyDADMAC of the invention has been shown to be especially useful as a fixative in papermaking applications. Today the papermaker is facing environmental, economic and quality pressures, which result in closure of water systems, lower basis weights, replacement of virgin fiber by recycled fiber and at the same time declining quality of recycled fiber and higher ash contents therein. These factors have resulted in furnish which is high in colloidal dispersions. The ultra high molecular weight polyDADMAC of the invention shows particularly good performance in papermaking applications where fixation of colloidal hydrophobic dispersion resulting from pitch, “white pitch” or “stickies” is important.